KR100294062B1 - Clamp ring for domed pedestal in wafer processing chamber - Google Patents

Abstract

A chamber for processing a semiconductor wafer surrounds a domed pedestal for supporting the wafer therein and a clamp in which a sheet is formed. The sheet receives and supports the outer periphery of the wafer on the domed pedestal and includes a wafer bonding surface that engages and supports the outer periphery of the wafer. In use, the wafer bonding surface forms an angle greater than or equal to the angle at which the tangent to the domed pedestal is horizontal, in that the wafer outer periphery is supported on the pedestal. Typically the angle parallel to the sheet is about 3 ° greater than the tangential angle to the domed pedestal in that the wafer is supported on the pedestal.

Description

Clamp ring for domed heating pedestal in wafer processing chamber

1 is an exploded view showing the inside of a thermal reactor for semiconductor processing in a partial section in the prior art.

FIG. 2 is a detail of the clamp ring shown in FIG. 1 showing how the ring secures the surface of the wafer.

3 is a cross-sectional view similar to FIG. 2 for explaining one embodiment of the present invention.

4 is a view similar to FIG. 3 for explaining another embodiment of the present invention.

5 is a plan view of the way support ring and the domed pedestal.

6 is a sectional view along line 6-6 of FIG.

<Description of the symbols for the main parts of the drawings>

6; Cutting axis 10: wafer

12: support 18, 58: pedestal

14: flat support surface 16, 56: lift finger

20, 60: groove 19: common central axis

31 sheet 26 annular sheet

34, 44: wafer bonding surface 24, 32, 42: clamp ring

30, 40, 50: edge 54: wafer support surface

The present invention relates to a semiconductor wafer processing reactor, and more particularly to an improved clamp ring for clamping a semiconductor wafer onto a domed heating pedestal used in the processing reactor.

Semiconductor wafers are generally processed in thermal reactors, and wafers go through many different processing steps. In wafer processing such as, for example, physical vapor deposition (PVD), called sputtering, the wafer to be processed is supported on a domed heating pedestal by a clamping device of the same kind as a clamp ring. More details about the PVD / sputtering process itself and the apparatus used in the process are disclosed in US Pat. No. 5,108,569 (Gilboa et al.).

A typical PVD wafer processing reactor and how the wafer is mounted in the reactor prior to the start of processing is described with reference to FIG. 1, which is a cross-sectional view of reactor related internal components.

Prior to the start of wafer processing, the semiconductor wafer 10 is moved transversely into the reactor by a robot arm (not shown). The horseshoe-shaped wafer support 12 then holds the wafer 10 until the wafer is lifted off the robot arm and four lift fingers 16 (only two of which are shown) are supported by the flat support surface 14. ) Comes up from below. In this position the robotic arm lies in the opening 17 of the horseshoe support. The robotic arm then leaves the reactor and the horseshoe support 12 continues to rise. At the same time, the wafer heating pedestal 18 rises vertically to a position near the bottom surface of the wafer 10. As shown in this figure, the horseshoe-shaped support 12 and pedestal 18 both rise vertically (downward at the end of the process) along a common centerline, indicated by a dashed line.

Pedestal 18 has a domed top surface and has an outer diameter slightly smaller than the outer diameter of wafer 10. Four cutouts 20 are formed on the sides of the pedestal for the pedestal 18 to rise through the center of the support 12 and exit the lift fingers 16. These grooves are large enough to accommodate the fingers 16 as the pedestal 18 moves closer to the bottom of the wafer 10.

Pedestal 18 is typically made of stainless steel and includes a heater member for heating pedestal 18, although not shown. The heater heats the wafer 10 during the processing process. In order to uniformize the heat transfer of the wafer from the pedestal, gas is injected into the space between the pedestal and the wafer through the gas conduit 22 formed in the pedestal 18 and discharged at the center of the domed surface of the pedestal. A more detailed description of this method is given below.

The horseshoe-shaped support 12 lifts the wafer until it comes close to, but not in contact with, the generally circular clamp ring 24. The pedestal 18 then pushes down the wafer 10, causing the wafer to fall off the plane 14 of the lift fingers 16 and contact the annular seat 26 formed in the clamp ring 24.

The pedestal 18 continues to rise until the clamp ring 24 is lifted off its support (not shown) and supported only by the wafer 10 lying on the pedestal 18. Since the clamp ring 24 is quite heavy (approximately 3 pounds or 1.35 kilograms), the wafer fits the contour of the dome of the pedestal 18. This configuration is shown in greater detail in FIG. 2, which is an enlarged detail of the area where the clamp ring 24 engages the edge of the wafer 10. At this location the PVD / sputtering step takes place.

Figure 2 clearly illustrates the problem associated with the clamp ring of the prior art. As is apparent from this figure, the sheet 26 is horizontal, while the wafer suitable for the pedestal and the shape of the pedestal is curved. As a result, the contact between the heavy clamp ring 24 and the wafer 10 is a sharp right angled edge 30. The problem associated with this arrangement is that the edge 30 may be grooved roundly in the wafer, which may damage the surface of the wafer. Such damage may result in the generation of unwanted particles during the process, and a stain line may be formed causing chipping or flaking of the layers (deposited during continued wafer processing) on the surface. do.

The problems become larger when gas is injected into the gas conduit 22. This gas is used to ensure a uniform heating of the wafer and is forced into the space between the back of the wafer 10 and the pedestal 18. Inert gases such as argon, usually in the space behind the wafer, are typically at a pressure of 4 to 12 Torr, whereas the inside of the reactor is 4 to 10 milliTorr. Because of this pressure difference, the wafer flexes flexibly away from the pedestal 18, with the largest separation between the wafer and the pedestal at the center of the wafer, the location indicated by the dotted line 10 '. This flexibility not only increases the pressure exerted on the surface of the wafer by the edge 30 of the clamp ring 24, but also allows the outer edge of the wafer to move towards the center due to the flexibility of the wafer, thereby resulting in an edge 30. ) Scratches the surface of the wafer 10.

Attempts have been made in the past to overcome this problem by very accurate machining and in particular by the precise grinding of the sheet 26 and the right angled edge 30. Such machining and polishing requires careful work by a skilled technician and is therefore very expensive.

Unfortunately, even the most carefully polished and consequently clean right angle edge 3 is not sufficient to provide a flawless edge 30 as a whole. This imperfection at the edge 30 acts as a stress concentration point when the wafer is supported on the pedestal. These concentration points cause damage that can be particularly problematic because silicon wafers have properties similar to glass pieces; That is, a small chip or score mark on the wafer surface spreads out from the stress point and makes the wafer unruly. Scoring and marking of the wafer surface also destroys its planarity. Thus, for example, a series of treatments performed with materials such as tungsten-CVD, which are difficult to adhere to the surface of the wafer even under ideal conditions, cannot be achieved with some degree of reliability because tungsten cannot adhere to the damaged points of the surface. Do. As a result, tungsten will float on the entire surface of the wafer during subsequent processing.

Other problems associated with reactor components include unstable wafer support conditions due to incorrect positioning of the horseshoe support 12 and fingers 16 with open ends. This second problem is due to the manufacturing method of the support 12, i.e. the manufacturing method in which the support is first processed and then the fingers 16 are welded thereon. Unfortunately the welding is very difficult to achieve correctly and therefore the fingers are misaligned.

Therefore, there is a need for an improved method for clamping semiconductor wafers on domed pedestals in a thermal reactor as well as improving the construction of some of the other components in the reactor.

It is therefore an object of the present invention to provide an improved thermal reactor for processing wafers for semiconductors. The reactor includes a domed pedestal for supporting the wafer and controlling the temperature of the wafer, and a clamp ring having an annular sheet formed therein to receive and support the outer periphery of the wafer for semiconductors over the domed pedestal. The sheet formed in the clamp ring is held in engagement with the outer circumference of the wafer and, in use, the wafer bond formed so as to be defined at an angle equal to or greater than the tangential elevation of the tangent to the domed pedestal in that the outer circumference of the wafer is supported on the pedestal. Contains cotton.

It is desirable to define an angle of 4 ° with respect to the horizontal. The angle is typically 3 ° greater than the elevation angle to the domed pedestal in that the wafer is supported on the pedestal.

In addition, the inner edge of the sheet can be formed with rounded corners, thus reducing the possibility of scratching the surface of the wafer.

The present invention has the advantage that the sheet supporting the outer periphery of the wafer over the domed pedestal occupies much more surface area on the top surface of the wafer than prior art devices.

Another advantage of the present invention is that no sharp edges in the clamp ring touch the wafer surface. Thus, wafer surface damage is minimized.

Various advantages of the invention will be apparent to those skilled in the art from the description of the preferred embodiment shown in the several drawings.

3 is a cross-sectional view illustrating how the semiconductor wafer 10 is secured onto the domed pedestal 18 by the stainless steel clamp ring 32 of the present invention.

As shown, the clamp ring 32 has an annular sheet 31 therein. The sheet 31 includes a wafer bonding surface 34 and an inclined sidewall 36. Wafer mating surface 34 is approximately 0.071 "(1.8 mm) wide and supports the outer periphery of wafer 10 over domed heating pedestal 18 similar to that shown in FIG. And a roof portion formed concentrically with the wafer mating surface 34 but located therein.

As in the apparatus shown in FIGS. 1 and 2, the wafer has a domed contour that corresponds to the contour of the dome of the pedestal 18 when it is clamped onto the pedestal. However, in the present invention, the wafer engagement surface 34 is formed to define the angle of α with respect to the horizontal line when the surface is in use. This angle α is larger than β. β is the angle between the tangent to the domed pedestal at the point where the wafer is supported above the pedestal 18 and the horizontal line, ie the plane perpendicular to the central axis 19 through which the parts move. As shown in this figure, the curvature of the dome is greatly exaggerated for the city. The α angle is preferably at least 1 ° larger than the β angle. In fact, the β angle is about 1 °. Usually, the angle α is about 4 °.

As a result of this arrangement, when gas is injected into the space between the back of the wafer 10 and the pedestal 18 (as described with reference to the prior art) and the wafer is inflated to the position 10 'indicated by the dotted line. The actual amount of contact area is indicated by the wafer bonding surface 34 on the upper surface of the wafer. Also, since the α angle is much larger than the β angle, considerable flexibility is allowed in the wafer 10 before the inner edge 40 of the wafer bonding surface 34 contacts the surface of the wafer.

Since the outer periphery of the wafer is supported by a flat surface as opposed to being supported by the sharp edge of the prior art device, the marking of the wafer upper surface is significantly reduced. In addition, the clamp ring of the present invention supports the outer periphery of the wafer on the pedestal 18, resulting in a better seal between the outer periphery of the wafer and the pedestal, thereby reducing the amount of pressurized gas escaping from the bottom of the wafer. Thus, the pressure of the gas can be increased by 6% to 10%, thereby allowing the surface of the wafer to be heated more evenly.

From this figure the side wall 36 of the clamp ring is angled from vertical to back. Usually the said angle is about 10 degrees. The angled sidewalls 36 define the outer edge of the wafer mating surface 34, and at the same time guide the wafer and pedestal ascending toward the clamp ring 32.

Another embodiment of what is described in FIG. 3 is shown in FIG. In FIG. 3, the clamp ring 42 has a wafer engagement surface that is angled at about 1 ° with respect to the horizontal plane. The angle is still greater than or equal to the β angle (between the tangent and the horizontal plane), so that the wafer 10 can bend to position 10 '. The clamp ring 42 has a side wall 46 and a roof portion 48 similar to the corresponding portions in FIG. 3.

In addition, the inner edge 50 of the wafer mating surface 44 is rounded to approximately 0.023 "(0.58 mm) or larger radius of curvature. Due to this shape, the flexible wafer is driven by a rounded surface rather than a sharp 90 ° edge. The shape thus reduces the likelihood of damage to the wafer top surface.

In FIGS. 5 and 6, referred together herein, details of the improved wafer support ring 52 and the associated lift finger 56 are illustrated. In Figure 5 it can be seen that the wafer support ring 52 has the form of a continuous ring, unlike the horseshoe shape of the support according to the prior art. The position of the heater pedestal 58 is shown in FIG. 5 (in dashed lines). The groove 60 in the pedestal 58 and the way in which the wafer lift finger 56 fits in this groove are very clearly shown in this figure.

5 and 6, it can be seen that the wafer support ring 52 can be attached to a standard lifting mechanism (not shown) on the side of the attachment tab 62 on one side of the ring. This is usually accomplished by riveting the tab 62 to the lifting mechanism.

A stepped brace 64 is made between the arms of the horseshoe type wafer support ring 52 opposite the tab 62 against the wafer support ring 52. The stepped brace 64 effectively lowers the top of the wafer support ring 52 in this section and provides an entrance for the robotic arm to insert and remove the wafer from the thermal reactor. Without the stepped braces, horseshoe supports of the prior art would be needed. It is clear that a closed ring will provide much stronger support than a horseshoe with an open end.

In particular the lift fingers seen in FIG. 6 have a wafer support surface 54 that will lift the wafer from the robotic arm. In order to make this process and to ensure that the wafer is correctly positioned on the lift finger, each lift finger 5 ^ has an inclined surface 66 which serves to guide the wafer to a position on the wafer support surface 54. To ensure that the fingers themselves are correctly positioned on the ring, the fingers are welded onto the ring during the initial machining step. The ring is machined with the finger so that it is precisely positioned on both the wafer support ring and the clamp ring that will interact while raising and lowering the wafer.

Although the present invention has been described above by means of specific embodiments, it is anticipated that other and modified embodiments therefrom will no doubt be apparent to the partner. For example, the present invention can be applied to a wafer etching apparatus, where an intermittent mating surface is provided instead of a continuous wafer mating surface 34. In addition, pedestals can be used for cooling as well as for heating. In addition, the precise shape of the dome is not critical to the invention, and the wafer may be a substrate in the form of another material, not just a semiconductor wafer. Therefore, the following claims are intended to cover all other and modified embodiments that fall within the spirit and scope of the present invention.

Claims (16)

A clamp for supporting a substrate being processed against a domed pedestal, comprising: an outer peripheral section defining an inner aperture to expose a major portion of the substrate; And an inner sheet surface formed on the outer circumferential portion to support the outer circumference of the substrate with respect to the domed pedestal, wherein the inner sheet surface in use is a domed peak of the pedestal from a surface perpendicular to the direction in which the substrate is supported relative to the domed pedestal. Tilted at a first angle α, the angle α being greater than the angle β from the vertical plane to the tangent to the domed pedestal at the point at which the substrate is supported relative to the domed pedestal. Clamp characterized in that. The clamp of claim 1 wherein the domed pedestal has a rounded upper domed surface and the inner city surface is annular. A clamping assembly for supporting a substrate during processing, the clamping assembly comprising: a substrate support comprising a substrate receiving surface that is generally symmetric about a first axis; And a clamp that is movable relative to the substrate support along the first axis, the clamp including a mating surface for engaging the outer peripheral portion of the substrate with respect to the substrate receiving surface at the contact portion to hold the outer peripheral portion of the substrate. The clamping assembly, characterized in that it has an angle greater than 0 degrees upward toward the support surface. 4. The clamping assembly of claim 3 wherein said angle is between one half and four degrees. 5. The clamping assembly of claim 4 wherein the angle is in a range between 1 degree and 3 degrees. A substrate processing apparatus, comprising: a chamber; A pedestal having a substrate support surface for supporting a substrate inside the chamber; And a clamp defining a perimeter of the substrate, the clamp including a seat having a substrate engaging surface for engaging and retaining the outer circumferential portion of the substrate over the supporting surface, wherein the engaging surface is greater than zero degrees with respect to the supporting surface in use The substrate processing apparatus which defines an upper inner angle. 7. The substrate processing apparatus of claim 6, wherein the angle is between ½ degree and 4 degrees. 8. The substrate processing apparatus of claim 7, wherein the substrate joining surface has an inner edge having a rounded corner. 9. The substrate processing apparatus of claim 8, wherein the pedestal and the clamp have a common axis, the pedestal and the clamp move relative to each other along the common axis, thereby clamping the substrate therebetween. The apparatus of claim 9, wherein the substrate processing apparatus further comprises a gas conduit formed in the pedestal for discharging at the boundary between the pedestal and the substrate, wherein the gas conduit injects gas at the boundary between the pedestal and the substrate, And the gas lifts at least a portion of the substrate from the substrate support surface. The substrate processing apparatus of claim 10, wherein the pedestal comprises a heater member that heats the pedestal to heat the gas and the substrate in use. The substrate processing apparatus of claim 6, wherein the substrate support surface is domed. A clamp for supporting a substrate being processed against a domed pedestal, the clamp comprising: an outer periphery defining an interior aperture for exposing a major portion of the substrate; And an inner sheet surface formed on the outer circumference to support the outer circumference of the substrate with respect to the pedestal, the inner sheet surface including an inner edge with rounded corners, the inner sheet surface being in use in a direction in which the substrate is supported relative to the domed pedestal. From the vertical line to the dome-shaped peak of the pedestal toward the first angle α, the first angle α from the vertical line to the tangent to the domed pedestal at the point at which the substrate is supported relative to the domed pedestal. A clamp, characterized in that it is larger than the angle β. The clamp of claim 1, wherein the seat surface includes an inner edge with rounded corners. 4. The clamping assembly as claimed in claim 3, wherein the engagement surface includes an inner edge with a rounded corner. 6. The clamping assembly of claim 5 wherein said substrate receiving surface is domed.